Condensation cross-linking polysiloxane masses, a process for preparing the same and surface-modified fillers

ABSTRACT

The present invention relates to polysiloxane compositions which cross-link by condensation and contain at least one cross-linkable polysiloxane, at least one basic filler, at least one phosphorus compound, at least one alkoxysilane cross-linking agent, at least one organometallic compound and optionally other auxiliary substances, a process for their production and their use, as well as surface-modified fillers and their use.

The present invention relates to polysiloxane compositions whichcross-link by condensation and contain at least one cross-linkablepolysiloxane, at least one basic filler, at least one phosphoruscompound, at least one alkoxysilane crosslinking agent, at least oneorganometallic compound and optionally other auxiliary substances, aprocess for their production and their use, as well as surface-modifiedfillers and their use.

The polysiloxane compositions according to the invention, referred tohereinafter as RTV-1 (Room-temperature vulcanizing 1-component) alkoxysystems, are compositions which are storable with the exclusion ofmoisture and cure to form elastomers on exposure to atmospheric moisturewith the elimination of alcohols.

Products of this kind have been known for a very long time and have beenwidely used on the market as sealants. The production of suchcompositions from OH— or alkoxy-terminated polysiloxanes, optionallyunreactive polysiloxane plasticizers, alkoxysilane cross-linking agents,catalysts, fillers and optionally other auxiliary substances is knownfrom U.S. Pat. No. 3,294,739, U.S. Pat. No. 3,161,614 and U.S. Pat. No.3,494,951.

The material costs of RTV-1 compositions can be considerably reduced bythe use of fillers. The fillers do however not only render thecompositions less costly but they also substantially influence theproperties of the RTV-1 alkoxy systems. The concentration andcomposition of the fillers used has a crucial effect on the rheologicalproperties of the unvulcanized compositions, such as their thixotropyand flow behaviour. They are furthermore important for the mechanicalproperties of the cured vulcanizates, such as their tear resistance,elongation at break and modulus of elasticity. Chalks are for examplevery frequently used as fillers for RTV-1 compositions. Ground naturalchalk is usually used together with pyrogenic silicic acid. The silicicacid is necessary in this combination if thixotropic compositions arerequired. Precipitated chalks may be used as an alternative. Thesechalks can likewise be combined with silicic acid and also with naturalchalk. However, in sufficient concentrations, they yield thixotropiccompositions even without silicic acid. Sealants which containprecipitated chalk are distinguished by high tear resistance andelongation at break as well as good adhesion and they are therefore verysuitable for the typical applications in the RTV-1 field, such as forexample as sealants.

The incorporation of fillers into RTV-1 compositions, in particular atelevated concentrations, can lead to a high increase in viscosity. Thishigh viscosity can cause difficulties in the production of thecompositions and also impair their processing. In addition, at highdegrees of filling, the modulus of elasticity of the cured sealantsincreases and their elongation at break is reduced. Precisely the use ofprecipitated chalks can lead to very high elastic moduli, which areundesirable for the use of the RTV-1 alkoxy systems as sealants. Onefurther disadvantage which can result from the use of the fillers, suchas for example the chalks and in particular the precipitated chalks inRTV-1 alkoxy systems, is the reduced storage life of the unvulcanizedpastes. If such RTV-1 products are stored with the exclusion ofatmospheric moisture and samples are taken from time to time, theircross-linkability suffers as a function of the storage time. Finallythey even completely fail to cross-link upon exposure to atmosphericmoisture. RTV-1 alkoxy systems generally have shorter storage lives thanother RTV-1 compositions. Due to the reduction in their shelf-lives theyonly have limited applicability.

The rheological properties of highly-filled RTV-1 polysiloxanecompositions can be improved by additives. Different additives have beendescribed in the literature for the various cross-linking systems. Apartfrom affecting the rheological properties and changing theincorporability of fillers, these additives also change the mechanicalproperties of the vulcanizates. They usually reduce the modulus ofelasticity. By the addition of such auxiliary substances other importantproperties of the products can however be impaired, such as for examplethe storage life of the unvulcanized compositions and their adhesiveproperties.

Sulphonic acids, and in particular dodecylbenzenesulphonic acid and itssalts, are known from EP-A-314 313 and EP-A 314 314 as suitableadditives. These sulphonic-acid-containing RTV-1 alkoxy systems resultin low moduli of elasticity of the vulcanizates, and the storage life ofthe unvulcanized products which, without the addition of the sulphonicacid, is relatively small, is not improved by the addition ofdodecylbenzenesulphonic acid.

In DE-A-2007002 etherified or esterified polyglycols are used in filledRTV-1 compositions. These products are prepared with the use of varioussilane crosslinking agents containing at least one nitrogen atom in themolecule, such as for example oximo-, amino- or aminoxysilanecross-linking agents. In DE-A-2 653 499, phosphoric acid esters aredescribed, in combination with the same crosslinking agents. Suitableadditives for alkoxy systems that have a low modulus of elasticity and agood storage life are not known.

The problem therefore existed of developing filled RTV-1 alkoxy systemsthat possess a low modulus of elasticity, high elongation at break andgood storage lives in their unvulcanized state. In addition, upon curingthey should adhere well to many substrates.

Surprisingly, it has now been found that the known disadvantages ofhighly-filled polysiloxane compositions that cure at room temperature onexposure to atmospheric moisture and release alcohols as cleavageproducts can be very largely eliminated if phosphoric acid esters and/orpolyphosphoric acid esters are added as additives to the compositions.By means of these additives, both the mechanical properties of the curedrubbers and their storage life in the unvulcanized state are markedlyimproved.

The present invention provides polysiloxane compositions whichcross-link by condensation and contain

-   a) at least one cross-linkable polysiloxane that contains as    reactive terminal group at least one of the following groups    —O—SiR¹ ₂OH, —O—SiR¹(OR²)₂, —O—Si(OR²)₃,    -   wherein    -   R¹ denotes optionally substituted C₁–C₈-alkyl, C₆–C₁₄-aryl or        C₂–C₈alkenyl groups and    -   R² denotes optionally substituted linear or branched C₁–C₈-alkyl        or C₂–C₈-alkoxyalkyl groups, and R¹ and R² may be the same or        different within the molecule,-   b) at least one basic filler and optionally other fillers,-   c) at least one phosphorus compound from the group comprising    orthophosphoric acid esters of the following formula I    O═P(OR³)_(3-n)(OH)_(n)    -   in which    -   n=0, 1 or 2 and    -   R³=an optionally substituted linear or branched C₁–C₃₀-alkyl,        C₁–C₃₀-acyl, C₂–C₃₀-alkenyl, C₂–C₃₀-alkoxyalkyl,        -   C₅–C₁₄-cycloalkyl or C₆–C₁₀-aryl group or a triorganosilyl            or diorganoalkoxysilyl group which can be the same or            different within the molecule,    -   and/or the esters of polyphosphoric acid,-   d) at least one alkoxysilane cross-linking agent of the formula    R¹ _(x)Si(OR²)_(4-x),    -   wherein    -   x=0 and 1, and R¹ and R² can be the same or different within the        molecule,-   e) at least one organometallic compound and-   f) optionally other auxiliary substances, such as for example    plasticizers, bonding agents, stabilizers, pigments, fungicides etc.

Cross-linkable polysiloxanes a) for the purposes of the invention arepolydiorganosiloxanes, preferably polydimethylsiloxanes, wherein themethyl groups may optionally be partially replaced by vinyl, phenyl, C₂to C₈ alkyl or haloalkyl groups. The polydimethylsiloxanes aresubstantially linear, but can contain small proportions of organosiloxyunits having a branching effect. In a preferred specific embodiment ofthe present invention the cross-linkable polysiloxane a) has a viscositybetween 0.1 and 1000 Pa·s, preferably between 10 and 500 Pa·s. Inaddition the cross-linkable polydiorganosiloxane a) can be partiallysubstituted by unreactive groups, such as for example trimethylsiloxygroups.

In a preferred specific embodiment of the present invention the reactivegroups of the polysiloxanes are—O—Si(R¹)₂OH groups, in which

-   R¹=an optionally substituted C₁–C₈-alkyl, C₆–C₁₄-aryl or    C₂–C₈-alkenyl group, and wherein R¹ may be the same or different    within the molecule.

The term substituted includes all the usual substituents, such as forexample halogen, NO₂, NH₂, amine, alkoxy, etc.

The basic fillers b) are for example precipitated or ground chalk, metaloxides, sulphates, silicates, hydroxides, carbonates andhydrogencarbonates. Other fillers are e.g. reinforcing andnon-reinforcing fillers, such as for example pyrogenic or precipitatedsilicic acid, carbon black or quartz powder. Both the basic fillers andthe other reinforcing or non-reinforcing fillers may optionally besurface-modified. Particularly preferred basic fillers b) areprecipitated or ground chalks. Component b) can also consist of mixturesof fillers.

The phosphorus compounds c) according to the invention are esters ofortho- and polyphosphoric acid or mixtures thereof. The esters oforthophosphoric acid are described by the following general formula;O═P(OR³)_(3-n)(OH)_(n),wherein

-   n=0, 1 or 2 and-   R³ denotes an optionally substituted linear or branched    C₁–C₃₀-alkyl, C₁–C₃₀-acyl, C₂–C₃₀-alkenyl, C₂–C₃₀-alkoxyalkyl,    C₅–C₁₄-cycloalkyl or C₆–C₁₀-aryl group or a triorganosilyl or    diorganoalkoxysilyl group, and R³ may be the same or different    within the molecule.

In a preferred specific embodiment of the present invention thephosphorus compound c) is an ester of orthophosphoric acid of theformula I, with at least one optionally substituted linear or branchedC₄–C₃₀-alkyl group R³. Where n=0 at least one of the substituents R³must be triorganosilyl or diorganoalkoxysily radical.

Examples of phosphoric acid esters c) according to the invention areprimary and secondary esters of orthophosphoric acid as well as mixturesthereof, such as di(2-ethylhexyl) phosphate, dihexadecyl phosphate,diisononyl phosphate, monodiisodecyl phosphate, mono(2-ethylhexyl)phosphate and tris(trimethylsilyl) phosphate.

Component c) can likewise be an ester of polyphosphoric acid or amixture of several polyphosphoric acid esters. Salts of partial ortho-and polyphosphoric acid esters, such as for example alkali metal salts,also are suitable.

Silane cross-linking agents, d) in the polysiloxane compositionsaccording to the invention are alkoxysilanes of the general formulaR¹ _(x)Si(OR²)_(4-x)in which

-   x=0 and 1,-   R¹ denotes optionally substituted C₁–C₈ alkyl, C₆–C₁₄ aryl or C₂–C₈    alkenyl groups and-   R² denotes optionally substituted C₁–C₈ alkyl linear or branched    C₁–C₈ alkyl or C₂–C₈ alkoxyalkyl groups, wherein R¹ and R² can be    the same or different within the molecule,-   or their mixtures.

Preferred alkoxysilanes are tetraethoxysilane, tetra-n-propoxysilane,methyltriethoxysilane, methyltrimethoxysilane, methyltri(2-methoxyethoxy)silane, vinyl trimethoxysilane orvinyltriethoxysilane. Methyl- and vinyltrimethoxysilane are preferred.Component d) can also be a partial hydrolyzate of the alkoxysilanecrosslinking agents.

All catalysts which are commonly used according to the prior art inRTV-1 compositions are suitable as organometallic compounds e). Organictitanium and tin compounds are particularly preferred. Cross-linkablepolysiloxanes a) containing the reactive groups—O—SiR¹(OR²)₂, —O—Si(OR²)₃are preferably used in combination with organic tin compounds, thegroups R¹ and R² having the meaning already mentioned. Particularlypreferred tin compounds are e.g. diorganotin dicarboxylates, such asdibutyltin dilaurate and dioctyltin maleate as well as solutions ofdiorganotin oxides in silicic acid esters. Preferred titanium compoundsare alkyl titanates, such as for example tetraisopropyl titanate ortetrabutyl titanate and chelated titanium compounds, such as diisobutylbis(ethyl acetoacetate) titanate, diisopropyl bis(acetylacetonate)titanate or diisopropyl bis(ethylacetoacetate) titanate.

Additives and auxiliary substances f) for the purposes of the inventionare preferably plasticizers, bonding agents, pigments and fungicides.

In a preferred specific embodiment of the present invention, theauxiliary substances f) are silicone plasticizers, such as for examplepolydimethylsiloxanes having terminal trimethylsiloxy groups and aviscosity of 0.1 to 5 Pa·s, bonding agents, such as for exampleorganofunctional silanes of the formulae:X—CH₂—CH₂—CH₂—Si(OR²)₃in which X=—NH—CH₂—CH₂—NH₂,

—O—C(O)—C(CH₃)═CH₂, —NH₂, —SH, —OH or —Cl and

-   R² has the meaning already mentioned above.

The silicone compositions according to the invention preferably consistof

-   100 parts by weight of a),-   10 to 250 parts by weight of b),-   0.1 to 25 parts by weight of c),-   1 to 30 parts by weight of d)-   0.1 to 20 parts by weight of e) and-   0 to 240 parts by weight of f).

The total quantity of auxiliary substances and additives f) preferablycomprises:

-   0–100 parts by weight of plasticizers,-   0–20 parts by weight of bonding agents,-   0–100 parts by weight of pigments and 0–20 parts by weight of    fungicides,    the sum of all the components f) in the mixture being at most 240    parts by weight.

The present invention also provides a process for the production of thepolysiloxane compositions according to the invention. The components a)to f) are mixed with the exclusion of moisture. Preferably thecomponents a), b) and c) are initially introduced and the othercomponents are then added.

The phosphorus compounds c) according to the invention are preferablyincorporated into the compositions in the course of the production ofthe polysiloxane compositions. In a particularly preferred specificembodiment of the present invention the basic fillers b) and thephosphorus compound c), optionally dissolved in a suitable solvent, aremixed in a preliminary operation. Water or polar or non-polar organicsolvents, such as for example alcohols and aromatic or aliphatichydrocarbons, can for example be used as suitable solvents.

The present invention also relates to surface-modified fillers which areobtainable by reacting at least one basic filler b) with at least onephosphorus compound c) from the group comprising orthophosphoric acidesters of the following formula IO═P(OR³)_(3-n)(OH)_(n),in which

-   n=0, 1 or 2 and-   R³=an optionally substituted linear or branched C₁–C₃₀-alkyl,    C₁–C₃₀-acyl, C₂–C₃₀-alkenyl, C₂–C₃₀-alkoxyalkyl, C₅–C₁₄-cycloalkyl    or C₆–C₁₀-aryl group or a triorganosilyl or diorganoalkoxysilyl    group which can be the same or different within the molecule,    and/or esters of polyphosphoric acid, if appropriate in a solvent.

R³ is preferably C₁–C₃₀-alkyl.

Preferred solvents are water or polar or non-polar solvents, such as forexample alcohols, aromatic or aliphatic hydrocarbons and/orpolydimethylsiloxanes. These surface-modified fillers are hydrophobic.

The present invention also relates to the use of the polysiloxanecompositions according to the invention as sealants, adhesives orcoating materials.

The present invention also relates to the use of the surface-modifiedfillers in polysiloxane compositions, plastics, such as for example PVC,thermoplastics, rubber, polysulphide sealants, polyurethanecompositions, paints or lacquers.

The following examples serve to illustrate the invention without,however, having any limiting effect.

EXAMPLES

General Procedure for the Preparation and Evaluation of the Compositions

The compositions were prepared in a 1-liter planetary mixer inaccordance with the examples listed hereinafter. After the preparationthe compositions were filled into plastic cartridges and sealed. Thematerial for the appropriate further tests was freshly extruded directlyfrom the cartridges.

The cross-linking behaviour of the polysiloxane compositions was testedon a glass plate, for which purpose the pastes were applied in a layerthickness of 2 mm to an area of 40×60 mm. After 24 hours the layer ofmaterial was cut, peeled off by hand and the underneath surface felt inorder to determine whether the layer had cured through to the glasssurface.

In order to determine the mechanical properties of the vulcanizates,layers of a thickness of 2 mm were produced from the pastes. Afterleaving the layers to cure for 14 days at 23° C. and 50% relativeatmospheric humidity the vulcanizates were tested according to DIN 53504. Their hardness was determined after leaving them to cure for 21days according to DIN 53 505.

The storage life of the products was evaluated by storing the pastes inan aluminium tube with a screw cap at 50° C. Samples were taken atone-weekly intervals and tested for cross-linking. If the samples wereperfectly cross-linked 1 week after the extrusion, the test wasconsidered to have been passed. The test for storage life at 50° C. is amethod which is commonly used for the evaluation of sealants. It is aquick test for determining the storage life of the products in practice.

Examples 1 to 8

In a planetary mixer, 44.0 parts by weight of a polydimethylsiloxanecontaining terminal Si(CH₃)₂OH groups which had a viscosity of 50 Pa·sat 25° C. were mixed with 45.0 parts by weight of a precipitated chalk(BET specific surface area 19 m²/g) which had been treated with stearicacid. Various phosphoric acid esters were added and dispersed in themixture to form a homogeneous paste. The following compounds were usedin the quantities listed in Table 1:

-   Example 1: di(2-ethylhexyl) phosphate-   Example 2: mono(2-ethylhexyl) phosphate-   Example 3: monoisodecyl phosphate-   Example 4: 1:1 mixture of mono- and di-isononyl phosphate-   Example 5: trimethylsilyl-di(2-ethylhexyl) phosphate-   Example 6: trimethylsilyl-di(2-ethylhexyl) phosphate-   Example 7: bis(trimethylsilyl)-mono(2-ethylhexyl) phosphate-   Example 8: tris(trimethylsilyl) phosphate

Subsequently 8.0 parts by weight of a polydimethylsiloxane containingterminal —O—Si(CH₃)₃ groups and 2.5 parts by weight ofmethyltrimethoxysilane were stirred in and the composition of the pastewas completed by adding 1.0 part by weight of diisobutylbis(ethylacetoacetate) titanate as well as 0.1 part by weight ofN-aminoethyl-3-aminopropyltrimethoxysilane.

The compositions of Examples 1 to 8 cured completely within 24 hours.The other properties of the compositions are shown in Table 1.

Comparative Example 9

The procedure of Examples 1 to 8 was repeated, the addition of thephosphoric acid ester being omitted. This composition was alsocompletely cured after exposure to moisture for 24 hours. The testing ofthe storage life and the mechanical properties did however show that theproduct had inadequate properties. The storage life of only 2 weeks at50° C. and the poor mechanical properties such as high hardness, lowelongation and a high modulus of elasticity, very greatly restrict thepossible use of such a product as a sealant.

Comparative Example 10

The procedure of Example 9 was repeated, with the addition of 1.5 partsby weight of dodecylbenzenesulphonic acid. The sealant layer curedcompletely within 24 hours. The storage life of the product does notdiffer from that of Comparative Example 5 without any additive and, atonly 2 weeks at 50° C., is inadequate. The mechanical properties of thevulcanizate are of a high standard and include high elongation at breakand a low modulus of elasticity (Table 1).

TABLE 1 Test results of Examples 1 to 10 Parts by Elongation ModulusTear Storage life¹⁾ Example weight of Shore A at break of elasticityresistance at 50° C. No. phosphate hardness [%] [N/mm² [N/mm²] [inweeks]  1 1.5 28 880 0.49 2.0  4  2 1.0 17 820 0.41 1.7 10  3 1.1 23 7800.45 1.7 10  4 1.3 23 780 0.46 1.8 10  5 1.0 33 630 0.63 2.0  6  6 1.2531 930 0.50 2.34  6  7 1.0 28 830 0.50 2.11 14  8 1.0 30 500 0.45 1.9914  9²⁾ — 35 640 0.67 2.6  2³⁾ 10²⁾ 1.5⁴⁾ 24 930 0.44 2.0  2³⁾ ¹⁾afterthe indicated time the products were still in a perfect condition²⁾comparative example ³⁾composition no longer cures after 3 weeks. Theproduct is highly defective. ⁴⁾dodecylbenzenesulphonic acid.

1. Polysiloxane compositions which cross-link by condensation and whichcomprise: a) at least one cross-linkable polysiloxane comprising as areactive terminal group at least one of the following groups—O—SiR¹ ₂OH,—O—SiR¹(OR²)₂, or—O—Si(OR²)₃, wherein R¹ denotes optionally substituted C₁–C₈-alkyl,C₆–C₁₄-aryl or C_(2–C) ₈-alkenyl groups and R² denotes optionallysubstituted linear or branched C₁–C₈-alkyl or C₂–C₈-alkoxyalkyl groups,and R¹ and R² can be the same or different within the molecule, b) atleast one basic filler and optionally other fillers, c) at least onephosphorus compound selected from the group consisting of i)orthophosphoric acid esters of the following formulaO═P(OR³)_(3-n)OH_(n) in which n=0, 1 or 2 and R³=an optionallysubstituted linear or branched C₁–C₃₀-alkyl, C₁–C₃₀-acyl, C₂–C₃-alkenyl,C₂–C₃₀-alkoxyalkyl, C₅–C₁₄-cycloalkyl or C₆–C₁₀-aryl group or atriorganosilyl or diorganoalkoxysilyl group and each R³ can be the sameor different within the molecule, and wherein when, n denotes 0, atleast one of the substituents R³ is a triorganosilyl ordiorganoalkoxysilyl radical, and ii)esters of polyphosphoric acid, d) atleast one alkoxysilane cross-linking agent selected from the groupconsisting of tetraethoxysilane, tetra-n-propoxysilane,methyltriethoxysilane, methyltrimethoxysilane,methyltri(2-methoxyethoxy)silane, vinyltrimethoxysilane,vinyltriethoxysilane and partial hydrolyzates thereof, e) at least oneorganometallic compound selected from the group consisting of organictitanium compounds and organic tin compounds and f) optionally otherauxiliary substances selected from the group consisting of plasticizers,bonding agents, pigments and fungicides, wherein the phosphorus compoundc) is an ester of orthophosphoric acid containing at least oneoptionally substituted linear or branched C₄–C₃₀-alkyl group R³. 2.Polysiloxane compositions which cross link by condensation, according toclaim 1, wherein the cross-linkable polysiloxane a) has a viscosity ofbetween 0.1 and 1000 Pa·s.
 3. Polysiloxane compositions according toclaim 1, wherein the basic fillers b) are precipitated or ground chalks.4. Polysiloxane compositions according to claim 1, wherein theorganometallic compound e) is an organic titanium or tin compound. 5.Polysiloxane compositions according to claim 1 consisting essentially of100 parts by, weight of a), 10 to 250 parts by weight of b), 0.1 to 25parts by weight of c), 1 to 30 parts by weight of d), 0.1 to 20 parts byweight of e) and 0 to 240 parts by weight of f).
 6. Polysiloxanecompositions according to claim 1, wherein the auxiliary substance f)has the following composition: 0–100 parts by weight of plasticizers,0–20 parts by weight of bonding agents, 0–100 parts by weight ofpigments, 0–20 parts by weight of fungicides, the sum of all thecomponents f) in the mixture amounting to a maximum of 240 parts byweight.
 7. Process for the production of the polysiloxane compositionsof claim 1, wherein the basic fillers b) and the phosphorus compound c),optionally dissolved in a solvent, are mixed in a preliminary operation.8. Sealants, adhesives or coating compositions, comprising a compositionof claim 1.